Summary: Challenge in Accurate Measurement of Fast Reversible Bimolecular Reaction
Kyril M. Solntsev and Dan Huppert
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-AViV UniVersity, Tel AViV 69978, Israel
Noam Agmon*
The Fritz Haber Research Center, Department of Physical Chemistry, The Hebrew UniVersity,
Jerusalem 91904, Israel
ReceiVed: December 22, 2000; In Final Form: March 28, 2001
Reversible bimolecular chemical reactions of the AB h A + B type were predicted theoretically to deviate
from exponential kinetics, obeying convolution kinetics at intermediate times and ultimately approaching
equilibrium as a power law, t-3/2, with a concentration-dependent amplitude. By careful application of time-
resolved fluorescence methods, we verify these predictions for excited-state proton transfer from 2-naphthol-
6,8-disulfonate to acidified water. The variation of the asymptotic amplitude with concentration is due
predominantly to screening of the proton-anion Coulomb potential, and this masks the many-body effects
on reversible binding itself. Better signal-to-noise in the long-time tails is required for clearly establishing
the asymptotic behavior.
1. Introduction
Chemical reactions occur over a vast range of time scales.1
Chemists routinely monitor reactions from femtoseconds (fs)
to hours. Historically, only slow chemical reactions could have
been monitored in the time domain, with samples regularly